Role of Calcium Ions As Doped-Hole Attractors in Destabilizing Charge-Ordered States in Mn Perovskites

Magnetization and resistivity measurements have been performed in (La1-xCax)(z)MnO3-delta perovskites as a function of x, z, and delta around the charge-ordered state. Fifty percent of Ca ions stabilize the charge-ordered state even for Mn4+ as low as 40% whereas reducing that impurity concentration to 35% results in a conducting ferromagnetic state even for 50% of Mn4+ ions. A model is proposed in which Ca ions act not only as suppliers of holes but as attractors of doped-in holes.